code: def tagstr2tree(
      s,
      chunk_label="NP",
      root_label="S",
      sep="/",
      source_tagset=None,
      target_tagset=None,
  ):
      """
      Divide a string of bracketted tagged text into
      chunks and unchunked tokens, and produce a Tree.
      Chunks are marked by square brackets (``[...]``).  Words are
      delimited by whitespace, and each word should have the form
      ``text/tag``.  Words that do not contain a slash are
      assigned a ``tag`` of None.
  
      :param s: The string to be converted
      :type s: str
      :param chunk_label: The label to use for chunk nodes
      :type chunk_label: str
      :param root_label: The label to use for the root of the tree
      :type root_label: str
      :rtype: Tree
      """
  
      WORD_OR_BRACKET = re.compile(r"\[|\]|[^\[\]\s]+")
  
      stack = [Tree(root_label, [])]
      for match in WORD_OR_BRACKET.finditer(s):
          text = match.group()
          if text[0] == "[":
              if len(stack) != 1:
                  raise ValueError(
                      f"Unexpected [ at char {match.start():d}"
                  )
              chunk = Tree(chunk_label, [])
              stack[-1].append(chunk)
              stack.append(chunk)
          elif text[0] == "]":
              if len(stack) != 2:
                  raise ValueError(
                      f"Unexpected ] at char {match.start():d}"
                  )
              stack.pop()
          else:
              if sep is None:
                  stack[-1].append(text)
              else:
                  word, tag = str2tuple(text, sep)
                  if source_tagset and target_tagset:
                      tag = map_tag(source_tagset, target_tagset, tag)
                  stack[-1].append((word, tag))
  
      if len(stack) != 1:
          raise ValueError(f"Expected ] at char {len(s):d}")
      return stack[0]
  
imports: import re
  from nltk.metrics import accuracy
  from nltk.tag.mapping import map_tag
  from nltk.tag.util import str2tuple
  from nltk.tree import Tree
label_desc: Use image node_id 3 for calling a global function with example usage: tagstr2tree(s, chunk_label, root_label, sep, source_tagset, target_tagset) and returns: stack